BTW, Jim.

Classical music

serious music following long-established principles rather than a folk, jazz, or popular tradition.
(more specifically) music written in the European tradition during a period lasting approximately from 1750 to 1830, when forms such as the symphony, concerto, and sonata were standardized.

Music for a found harmonium was written in 1984 by Simon Jeffes. My point was that it you did not know that it would sit happily in any traditional music (not song) session and is indeed included in the BBC's virtual session.